62 TRINIDAD AND TOBAGO BULLETIN. [XIX. 2.. 



Tillage. There is evidence that good cultivation, by loosening and 

 aerating the soil, not only improves the cane but actually reduces the 

 number of froghoppers present. Occasionally damage is reported follow- 

 ing immediately on the use of implements, particularly sub-soil ploughs, 

 but when one considers the time taken for the development of the 

 greatest injury, it is usually seen that the damage in these canes would 

 have appeared whether or not the implements had been used. 



Variety. No variety of cane is immune, but a few are more resistant 

 than others. "Uba" and "Badilla" are the most resistant, but are unfor- 

 tunately not generally considered suitable for cultivation. 



Presence of Pests and Diseases. A.s a general rule 20 froghoppers 

 per stool will produce visible signs of damage, and 50 to 100 per stool 

 will produce severe da-mage. Fields in poor condition suffer more from 

 a small number of insects than betber fields do from a larger infestation.. 



Root fungi are constantly found in blighted fields as well as various 

 insect pests of cane which weaken the cane and make it less resistant 

 to frogliopper attacks. 



A-llowing for changes in season and age of plants a field attacked one 

 year is more liable to be attacked in the following year than one 

 previously free. 



GENEPvAL PROBLEMS. 



The question of the relative importance of the adult and nympli 

 froghopper and of the root disease is discussed. 



The froghopper is considered as the most important cause of the 

 blight because of (1) its constant presence in blighted areas, (2) the 

 constant presence of streaks on the leaves in severe blighb, (3) the 

 occurrence of Wight in plant canes when no other complicating disease 

 is present, (4) the variation in time of the first appearance of blight 

 according to the date of the first brood, (ij) the periodicity of the 



blight. 



The adult is considered as more important than the nymph because 

 the blight is never severe until the streaking of the leaves has developed 

 and is at its worst shortly after the greatest flight of adults. Symptoms 

 of blight have been produced in canes, which have never had nymphs, 

 by caging on them a number of adults. 



In addition several of the symptoms of blight, including in particular 

 the narrowing of the cane, have been produced in normal canes by 

 imitating the leaf destruction of adult froghoppers by removing the 

 greater number of leaves from the cane. 



The spread of injury in the leaf from the original point of infection 

 indicates the possibility of some toxin or enzyme being introduced into 

 the plant. 



Root disease is considered as playing its most important part after- 

 the froghopper has damaged the cane and particularly after the second 

 brood, when the damage may cease to \>z periodic and continue to 

 increase entirely owing to the effect of root fungi. 



The attacks of root disease follow on the froghopper attacks which 

 are the prime cause of injury. 



